The present invention relates to a variable light distribution type automobile lamp, such as a fog lamp, capable of varying the range of diffusion of a flux of light by changing the position of one of two cylindrical lenses.
As shown in FIGS. 1(a) and 1(b), variable light distribution type automotive lamps have been provided with two lenses 50 and 51 disposed on the optical axis in the path of a flux of parallel light rays. The lenses 50 and 51, which have cylindrical lens steps formed at the same pitch, vary the light distribution pattern of the flux of irradiating light either by converging or diffusing the light rays, as shown in FIG. 2. A flux of irradiated parallel light rays (FIG. 1(a)) is formed by bringing the focuses F1 and F2 of the lens steps of the two lenses 50 and 51 into agreement by moving one of the two lenses 50 and 51 in the direction of the optical axis (i.e., the direction indicated by the arrow A), while a flux of diverging light rays (FIG. 1(b)) is formed by spacing the focus F1 and the focus F2 from one another.
However, in a lamp having such a lens system, deviation of the two lenses 50 and 51 having many cylindrical lens steps in the direction of pitch (i.e., in a direction perpendicular to the optical axis), as shown in FIG. 1(c), causes a deflection of the main flux of light S towards the side area in relation to the optical axis L. It is therefore necessary to adjust the two cylindrical lenses in the course of the assembly of the lamp to eliminate such a deviation of the lenses in the pitch direction.
On the other hand, if the flux of light is, for example, in a diverging state, the direction of the main flux of light cannot be determined, and, consequently, there is no flux of light that can serve as the reference. Hence, the adjustment of the lenses 50 and 51 not only requires a high degree of skill, but also the adjustment requires a great amount of time. Moreover, the driving mechanism for the lens system requires measures such as the provision of a correcting mechanism for preventing the cylindrical lens from deviating in the horizontal direction when the cylindrical lens on the light source side is driven. This presents such problems as complication of the overall structure of the lamp.
The present invention further relates to improvements in a driving device for a variable light distribution type automotive lamp capable of varying the range of diffusion of a flux of light in accordance with the speed of the vehicle.
A conventional variable light distribution type automobile lamp is known which is provided with two cylindrical lenses disposed on the optical axis forward of a parallel light flux irradiating device and which performs variable control over the light distribution pattern by converging or diffusing the flux of light passing through the lens in accordance with the vehicle speed by changing the relationship of the two lenses in terms of the positions of their focuses by controlling the movement of one of the lenses in the direction of the optical axis. This type of automobile lamp, which can thus produce a favorable distribution of light suitable for various operating conditions, has made an important contribution to safety in the operation of motor vehicles.
However, in this type of lamps, the two lenses are formed lo with many cylindrical lens steps formed side by side in order to diffuse the flux of light rightward and leftward. Hence, if the two lenses deviate in the lateral direction from their proper positions, the flux of light is caused to deflect rightward or leftward. Thus, a precise construction is required to ensure accuracy in the correspondence of the individual lens steps on the two lenses. This not only results in a complicated construction, but also requires a high degree of skill and a large amount of time for the assembly and adjustment of the lamp.